Jackie's list is thoughtful, but I'm not convinced organic agriculture is always better for water quality. For one thing, it will take a lot more land and water to come up with an equivalent amount of food, because the bugs, microbes, and weeds get some. People don't use crop protection chemicals just to be mean and stupid. For another, the use of animal wastes for fertilizer makes water borne diseases more of a problem, and makes precise control of nitrogen almost impossible, because of the more variable timing of the conversion into nitrate forms; and because the product itself is not uniform, so it can't be applied precisely. Finally, of course, the couple of billion humans whose lives depend on the synthesis of inorganic N to keep from starving to death will raise a ruckus prior to doing so, and that probably won't do Mother Earth much good, either. One heretical idea is that it makes sense for people to live and farm far away from sensitive headwaters and such. This requires storage and conveyance, but that's probably a fair trade-off. Imagine if all of LA, and all the farms and dairies in the Southern San Joaquin were jammed in between Redding and Sacramento instead of where the are. I suspect water quality would suffer.